1. Field of the Invention
This invention relates to surgery and more particularly to an apparatus and a method for identifying the original femorotibial joint location in a revision knee replacement.
2. Background of the Invention
The knee joint is made of a thigh bone (femur), a leg bone (tibia) and a knee cap (patella). The femur and the tibia are coupled at a femorotibial joint defined by a femorotibial joint plane.
A total knee arthroplasty or a total knee replacement is a surgical procedure wherein worn, diseased, or damaged surfaces of the knee joint are removed and replaced with artificial surfaces. When a patient has a total knee replacement, the distal end of the femur is severed and a femur prosthesis is implanted to the severed distal end of the femur. In a similar manner, the proximal end of the tibia is severed and a tibia prosthesis is attached to the severed proximal end of the tibia.
Typically, the femur prosthesis has a metallic surface whereas the tibia prosthesis has a plastic surface. The femur prosthesis and the tibia prosthesis provide a metal to plastic surfaces for articulating the knee joint of the patient at the femorotibial joint plane. In most cases the undersurface of the patella is also replaced with a plastic surface to articulate with the femoral surface at a junction is called the patellofemoral joint.
Total knee replacements appear to have an 80% to 90% survival rate for the designed useful life of twenty years. Approximately 10% to 20% of total knee replacements involve complications requiring the removal of the original prosthesis and the re-implantation of a new prosthesis. In addition, many of the successful total knee replacements must be replace after the expiration of the designed useful life of the prosthesis.
The re-implant of the new prostheses is referred to as a revision knee replacement. In the revision knee replacement, the femur prosthesis and the tibia prosthesis are removed and the new prostheses are implanted into the patient.
A revision surgery is more complex than the original knee replacement surgery. The revision surgery is more complex due to the difficulty of removing the original prosthesis and the quality and quantity of bone left behind after removal of the original prosthesis.
Among the most significant problems of a revision knee replacement surgery is the loss of the original femorotibial joint location. Since the distal end of the femur and the proximal end of the tibia were severed in the original nee replacement surgery, a void is present between the distal end of the femur and the proximal end of the tibia. The original femorotibial joint location as well as the orientation of the original rotation of the femur is not readily apparent to the surgeon.
If the second prosthesis is not properly located in the revision knee replacement surgery, the femur and the tibia will not be located and orientated properly relative to the collateral ligaments. The lack of a properly located and orientated femur and tibia with the collateral ligaments will restrict the range of motion of the knee joint for the patient.
Therefore, it is an object of this invention to provide an improved method and apparatus of identifying the original femorotibial joint location in a revision knee replacement of a patient.
Another object of this invention is to provide an improved method and apparatus for defining a femur reference plane to assist in establishing the correct rotation of the femur in a revision knee replacement of a patient.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by modifying the invention with in the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment of the invention.